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Registered User
Join Date: Oct 2015
Location: park City Utah
Posts: 5
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1986 Porsche 911 starting problem
So my friend Mike's 911 died on the road the other day after running perfectly for the summer, at first we thought fuel pump. We have started to diagnose and are stumped. The car turns over, gets a spark to coil and plugs, checked the fuel pump and it sprays fuel, checked the DME relay it clicks on and off, checked the ground strap on the transmission it is in place, and replaced the fuel filter. What are we missing? Could it be the motronic module went bad? We will be checking additional ground straps and other cables, but what should we look for in addition? Any help would be appreciated!
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10-16-2015, 05:04 PM
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Registered
Join Date: Sep 2012
Location: Newport Beach CA
Posts: 1,873
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Could be the sensors. There are a few current threads on trouble shooting the Motronic system. Look for screen name 'ischmitz'. He also repairs and tests the units.
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10-16-2015, 05:19 PM
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Brew Master
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Air, Fuel and Spark.
Check to make sure you're getting spark. If you have spark, get a fuel pressure test kit and check for fuel pressure (although it sounds like you've verified the fuel pump is working when it should) then get a noid light kit and make sure you have injector pulse. After reading again (without the aid of beer) I see you mention you have spark. If you have spark your speed and reference sensors are working. You mention the fuel pump works. Did you jumper it to get it to pump or how did you determine this? The fuel pump should only run when the car is cranking. For what it's worth, I checked my DME relay and swore it was working. I applied power to the coil and then verified the switches acted properly. After going through all sorts of steps I put a new DME relay in and the car fired right up. Last edited by cabmandone; 10-17-2015 at 02:24 AM.. |
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10-16-2015, 05:31 PM
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Registered Loser
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Get a new Porsche Brand DME relay FIRST. It's the reason 90% of the time.
__________________
Current Rides:: 1987 Red 911 Targa, 2007 R320 CDI, 2003 Red Dodge Ram Hemi, 1993 Beater Jeep Cherokee, Airbus A320 Gone but not forgotten: 1981 VW Scirocco S, 1989 Honda Accord Coupe LXI, F-16C (still my favorite vehicle!),MC-130P, C-130E, T-38, T-37, C150, C172, PA180 |
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10-16-2015, 05:35 PM
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Registered
Join Date: Sep 2012
Location: Newport Beach CA
Posts: 1,873
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10-16-2015, 05:40 PM
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Registered
Join Date: Sep 2012
Location: Newport Beach CA
Posts: 1,873
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10-16-2015, 05:46 PM
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Registered User
Join Date: Oct 2015
Location: park City Utah
Posts: 5
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New DME installed and still no joy...car cranks, gets a spark, but no running....Any suggestions?
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10-20-2015, 05:42 PM
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Registered
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I suggest troubleshooting instead of replacing parts based on probability of failure
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10-21-2015, 04:05 PM
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Brew Master
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Quote:
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10-21-2015, 05:00 PM
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Member 911 Anonymous
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Check the OHMs on the Ref/Speed Sensor.
To insure it is not the DME, please your DME into a donor car. DO NOT PUT THE DONOR DME INTO YOUR CAR. What is the voltage prior to cranking?
__________________
'85 Carrera Targa Factory Marble Grey/Black * Turbo Tail * 930 Steering Wheel* Sport Seats * 17" Fuchs (r) * 3.4 * 964 Cams * 915 * LSD * Factory SS * Turbo Tie Rods * Bilsteins * Euro Pre-Muff * SW Chip on 4K DME * NGK * Sienes GSK * Targa Body Brace PCA/POC |
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10-21-2015, 06:15 PM
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Registered User
Join Date: Oct 2015
Location: park City Utah
Posts: 5
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well after a long winter in hibernation we decided to bring the 911 down to Morris Brothers in SLC. The final diagnosis was a bad distributor that would not allow the engine to start. We are now having it rebuilt and hopefully on the road for the weekend.
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04-27-2016, 03:22 PM
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1985 Porsche 911 Cab
Marble Grey
